1. Field of the Invention
The present invention relates to an optometric apparatus for a subjective examination of a visual function (a visual acuity, etc.) of an eye of an examinee.
2. Description of Related Art
There is a red/green test (R/G test) as one of subjective examinations which are performed for prescribing the powers of spectacle lenses or contact lenses. This R/G test uses a red optotype and a green optotype having a red and green backgrounds adjacently placed, on each of which black figure targets and black character targets, identical between the red and green optotypes, are drawn or printed. This R/G test is performed for a check on final overcorrection or for a preliminary test of an astigmatism examination using a cross-cylinder. In this R/G test, the red and green optotypes are concurrently presented to an examinee (an examinee's eye) and the examinee is asked to tell a difference in vision between the optotypes, in other words, about which optotype is more clearly visible.
The R/G test, meanwhile, is regarded as effective for the eyes having little or small amplitude of accommodation (i.e., focusing ability of a crystalline lens), whereas the test would not be performed correctly on the eyes having a normal or large amplitude of accommodation because such eyes attempt to automatically accommodate during the test. Hence, Japanese patent unexamined publication No. Hei 10-179618 proposed a method in which a green optotype is presented to an examinee for a predetermined time or a green optotype is presented in a blinking state for a predetermined time and then the green optotype and a red optotype are simultaneously presented, and such steps are repeated while prompting an examinee to compare and respond about a difference in vision between the optotypes. According to this method, it is considered that the R/G test can efficiently be utilized when the automatic accommodation of the examinee is restrained as much as possible.
However, the test method disclosed in the above publication includes the particular steps of presenting the green optotype to the examinee for a predetermined time and then concurrently presenting the green and red optotypes. Thus, such test method could not be achieved by use of general-purpose optotype presenting devices commercially available at present.